When scanners mounted on multi-function peripherals (MFPs) are used, sheets are first set on original document stands (platens) in a state in which pressure plates (platen covers) are opened. Subsequently, the pressure plates are closed, but the scanners detect the widths of original documents by turning on light sources used to read original documents and located below the original document stands during closing the pressure plates. Simultaneously, the scanners detect the lengths of sheets by photo sensors. In the state in which the pressure plates are closed, the scanners scan the light sources used to read original documents in the longitudinal direction of sheets and guide reflected light up to CCDs. Then, the scanners capture images on the sheets by the CCDs.
In such scanners of the related art, there is a problem that light sources turned on during closing the pressure plates are dazzled.